There is known a technique for recognizing lane lines drawn on the road surface, making a vehicle travel along the traffic lane defined by the lane lines, and when the lane lines are not recognized, making the vehicle travel following a preceding vehicle (see Japanese Patent Application Publication No. 2004-206275).
However, if the vehicle simply follows the preceding vehicle; when the preceding vehicle does not travel along the traffic lane, the vehicle may not travel remaining at a predetermined position in the width direction of the traffic lane. This may decrease the reliability of the control to make the vehicle travel along the traffic lane, what is called lane keeping control.